A variety of physical and chemical techniques, chief among them being X-ray crystallography, will be applied to a series of T = 1 and T = 3 icosahedral viruses with the ultimate objectives of (1) deducing the detailed structure of the RNA genomes inside the viruses, (2) identifying important protein - nucleic acid interactions, and (3) devising a model for the assembly and disassembly of the virions consistent with existing biochemical and molecular biological data. The viruses to be studied are satellite tobacco mosaic virus (STMV), satellite panicum mosaic virus (SPMV), turnip yellow mosaic virus (TYMV), Desmodium Yellow Mottle Virus (DYMV), Tomato Aspermy Virus (TAV), Bromegrass Mosaic Virus (BMV), and empty capsids of each of the last four species. These six spherical viruses represent viruses whose structures are best known, for which RNA is visible in the virion, and for which the greatest amount of data and observations exist. Core RNA particles can be prepared by protease digestion of the intact viruses and their unfolding monitored by quasi elastic light scattering. Empty capsids can be made by freeze thawing and used in difference Fourier syntheses to reveal RNA structure. With the integration of chemical and enzymatic probe information and predictions from computer modeling a comprehensive understanding of structure and function will emerge. This research is significant because the conformation of the nucleic acid component of no spherical virus is currently known, and there is presently no comprehensive structural basis for the processes of viral assembly and disassembly.